Surface light source device

ABSTRACT

As regards a surface light source device for use with back-light or the like of a transmissive display panel, the efficiency of the cooling structure for the device will be improved and dust and dirt will be prevented from adhering. The surface-light source device has a housing, a diffuser panel, a reflective plate, lamps, and an electric circuit portion. The housing has a window portion located ahead, a base portion located behind and side portions forming a flat space by connecting the two. The diffuser panel is mounted to the window portion of the housing. The reflective plate is supported by the side portions and partitions the flat space into a closed space ahead and an open space behind to be interposed therebetween. The lamps are housed in the closed space, and are positioned right above the reflective plate and right under the diffuser panel to radiate light toward the diffuser panel. The electric circuit portion is housed in the open space, and is electrically connected to the lamps to light them up. On the side portions of the housing, there are formed openings, through which cooling air supplied from outside is introduced into the open space to diffuse heat accumulated within the housing.

This application is a Division of Ser. No. 08/940,978 filed Sep. 30,1997, now U.S. Pat. No. 5,993,027.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a surface light source device for usewith a back-light or the like for back-lighting a transmissive displaypanel, and more particularly to an air-cooled structure for a surfacelight source device containing lamps for allowing for heat conduction.

2. Description of Related Art

A display panel, using liquid crystal or the like as an electro-opticalsubstance in a large-sized flat display to replace CRT's, has been underdevelopment in recent years.

The display panel is not a spontaneous light emission type, butmodulates external light to display a screen. The display panel can beroughly divided into transmission types and reflection types. In thecase of the transmission type, a surface light source device is arrangedon the back of the display panel for back-lighting.

A surface light source device used as a back-light for A large-sizeddisplay panel contains lamps consisting of a large number of fluorescenttubes or the like to generate a large amount of heat. This heat raisesthe temperature of the display panel to change the electro-opticalcharacteristics of the liquid crystal used as electro-optical substance,thus deteriorating the image quality. Also, the atmospheric temperaturewithin the back-light rises to decrease the luminous efficiency of thefluorescent tubes, causing deteriorated brightness. For this reason,forced cooling using air-cooling fans or like becomes indispensable in alarge-sized back-light. If, however, an air-cooling fan is used, dust iswhirled up to adhere to the surface of lamps or to a diffuser paneldisposed thereon, thus deteriorating the uniformity of brightness of thesurface light source device.

If dust stuck on the lamps and the diffuser panel is visually recognizedby an observer through a transmissive display panel, the image qualitywill be noticeably deteriorated.

SUMMARY OF THE INVENTION

In order to solve the problem of the prior art described above, thefollowing measures were taken. That is, a surface light source deviceaccording to the present invention has, as its basic structure, ahousing, a diffuser panel, a reflective plate, lamps, an electriccircuit portion, and a heat-radiating portion. The housing has a windowportion located ahead, a base portion located behind and side portionsforming a flat space by connecting the two. The diffuser panel ismounted to the window portion. The reflective plate is supported by theside portions and partitions the flat space into a closed space aheadand an open space behind to be interposed therebetween. The lamps arehoused in the closed space, and are positioned right above thereflective plate and right under the diffuser panel to radiate lighttoward the diffuser panel. The electric circuit portion is housed in theopen space, and is electrically connected to the lamps to light them up.As the special feature, the heat-radiating portions are formed on theside portions of the housing, include a plurality of openings forconductively connecting to the open space, and introduce cooling airsupplied from outside into the open space to diffuse heat accumulatedwithin the housing.

Preferably, the reflective plate consists of an aluminum plate, on thesurface of which heat-resistant white coating has been applied, andtransmits the heat from the lamps generated on the front closed spaceside to the rear open space side to improve the cooling effect. Also,preferably, the reflective plate has a corrugated cross-section toreduce the resistance of cooling air flowing along its back surface toincrease the cooling effect. Further preferably, the reflective plate isone sheet of metal plate subjected to folding twice or more, or oneobtained by joining together metal pieces divided into two or moreparts, and sticking heat-conductive metal webs along the joints toeliminate any temperature differences between each metal piece. Inaddition, preferably, the lamps have a longitudinal shape havingelectrode portions at both ends thereof.

Protective members having heat conductivity and heat resistance aremounted to the electrode portions respectively in such a manner that theheat generated in the electrode portions is diffused outside of theclosed space through the protective members.

In the air-cooled structure according to the present invention, a closedspace (lamp house) is constituted between a diffuser panel and areflective plate which are installed in a housing, and lamps are housedtherein. Also, an open space is formed between the reflective plate andthe base portion of the housing, and cooling air is forcibly fed thereby an air-cooling fan or the like. Since the lamp house is closed uptight, there is no possibility that dust and dirt carried by cooling airenter can. Since the cooling air is blown along the back surface of thereflective plate, the air-cooling efficiency is high.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing an embodiment of a surface lightsource device according to the present invention;

FIG. 2 is a plan view schematically showing the surface light sourcedevice shown in FIG. 1;

FIG. 3 is an exploded perspective view showing an example of a flatdisplay set in which a surface light source device according to thepresent invention is installed as back-light; and

FIG. 4 is a sectional view showing an example of a transmissivedisplay-panel installed in the flat display set shown in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, the detailed description will be made of the bestembodiment according to the present invention with reference to thedrawings. FIG. 1 is a schematic, sectional view showing an embodiment ofa surface light source device according to the present invention. Asshown in the figure, a surface light source device 0 has a housing 1, adiffuser panel 2, a reflective plate 3, lamps 4, an electric circuitportion 5 and a heat-radiating portion. The housing 1 has a windowportion located ahead, a base portion 6 located behind and side portions7 forming a flat space by connecting together the two. The diffuserpanel 2 is mounted to the window portion of the housing 1. For thisdiffuser panel 2, obscure glass or the like can be used, or one obtainedby forming material, in which finely divided particles having lightdiffusion properties are dispersed in transparent resin such as acrylic,into a plate shape may be used. The reflective plate 3 is supported bythe side portions 7 for facing each other within the housing 1 andpartitions the flat space into a closed space (lamp house) 8 ahead andan open space 9 behind so as to be interposed therebetween. The lamps 4consist of fluorescent tubes or the like, and are housed in the closedspace 8. A plurality of lamps 4 are arranged at a fixed pitch, andpositioned right above the reflective plate 3 and right under thediffuser panel 2 to radiate light toward the diffuser panel 2. Thelight: from the lamps 4 as a light source is diffused by the diffuserpanel 2, and thereafter is emitted outward as luminous light havinguniform brightness distribution. Thus, the surface light source device 0having uniform brightness distribution can be obtained. The electriccircuit portion 5 is housed in the open space 9, and is electricallyconnected to the lamps 4 to light them up. If fluorescent tubes or thelike are used for the lamps 4, an inverter or the like is included inthe electric circuit portion 5.

As the special feature of the present invention, the heat-radiatingportions are formed in the side portions 7 of the housing 1, include aplurality of openings 7a and 7b for conductively connecting to the openspace 9, and introduce cooling air supplied from outside by anair-cooling fan or the like into the open space 9 to diffuse heataccumulated within the housing 1. In the example shown, the cooling airintroduced from the one opening 7a moves within the open space 9 alongthe back surface of the reflective plate 3, and is fed out through theother opening 7b.

As described above, in the present embodiment, a closed space (lamphouse) 8 is formed between a diffuser panel 2 and a reflective plate 3which are installed in the housing 1, and lamps 4 are housed therein.Accordingly, there is no possibility that dust and dirt fed in togetherwith the cooling air enter the closed space 8, making it possible toprevent dust and dirt from adhering. On the other hand, an open space 9is formed between the reflective plate 3 and the base portion 6 of thehousing 1, and cooling air is forcibly fed there by an externalair-cooling fan or the like. Since the cooling air moves along the backsurface of the reflective plate 3, it becomes possible to diffuse theheat generated from the lamps 4 outward very efficiently. In addition,the cooling air is capable of cooling also the electric circuit portion5 mounted on the base portion 6 of the housing 1.

Preferably, the reflective plate 3 consists of an aluminum plate, on thesurface of which heat-resistant white coating has been applied, andtransmits the heat from the lamps generated on the front closed space 8side to the rear open space 9 side to improve the cooling effect. Also,preferably, the reflective plate 3 has a corrugated cross-section convextoward below to reduce the resistance of cooling air flowing along itsback surface for increasing the cooling efficiency. In this respect, inthe present embodiment, the reflective plate 3 is obtained by joiningtogether metal pieces divided into two or more parts, and stickingheat-conductive metal webs 11 along the joints, or one sheet of metalplate may be folded. In a surface light source device corresponding to adisplay panel having a large screen, the area itself of the reflectiveplate 3 also becomes rather large. In such a case, it requiresengineering skill of a high order and is not so good in themanufacturing efficiency to form one sheet of reflective plate 3 into acorrugate shape. Therefore, as in the present embodiment, it ispractical to join together metal pieces divided in advance for workinginto a reflective plate 3. In this respect, the present invention is notrestricted to this, but the reflective plate 3 may be formed as solidstructure in a small-sized surface light source device. In the case ofthe reflective plate 3 divided, heat:-conductive metal webs (forexample, copper foil) 11 are so stuck along the joints as not tointercept the heat transfer at the joints. By so doing, the temperaturedistribution is made uniform over the entire surface of the reflectiveplate 3. The lamps 4 such as fluorescent tubes havetemperature-dependent properties in the light emission intensity and thelife. Therefore, in order to obtain uniform brightness distribution inthe surface light source device 0, it is necessary to make thetemperature distribution uniform over the entire closed space 8. To thisend, it is necessary to enhance the thermal conductivity of thereflective plate 3 in the surface direction, and in the case of thedivided reflective plate, the heat-conductive metal webs 11 stuck alongthe joints act effectively. Also, in order to make the lives of theindividual lamps 4 even, it is preferable to enhance theheatconductivity of the reflective plate 3 and to make the temperaturedistribution in the closed space 8 uniform.

FIG. 2 is a-plan view-schematically showing the plane shape of the,surface light source device 0 shown in FIG. 1. In the housing 1, thereflective plate 3 is mounted, on top of which a plurality of lamps 4are arranged. The individual lamps 4 consist of longitudinal-shapedfluorescent tubes equipped with electrode portions 12 at both endsthereof respectively. Each lamp 4 is supported at both ends by a pair ofholders 13. These lamps 4 are covered with the diffuser panel 2. In thehousing 1, partition walls 14 are installed on both sides. The centralportion enclosed with a pair of partition walls 14 constitutes theclosed space (lamp house) 8 described above. The portions outside ofeach partition wall 14 belong to the open space. In this open space,there is arranged a connector circuit 5a which becomes a part of theelectric circuit portion 5 (See FIG. 1). To this connector circuit 5a, aplurality of connectors 5b are installed, and are connected to theelectrode portions 12 for each lamp 4. In the present embodiment, theelectrode portions 12 for the lamps 4 are mounted with protectivemembers 15 having heat conductivity and heat resistance. However, onlyone protective member 15 is exemplified. The heat generated in theelectrode portion 12 is radiated outside the closed space through theprotective member 15. For the protective member 15, there can be used amolded product from rubber material having heat resistance and heatconductivity.

FIG. 3 is an exploded perspective view showing an example of a flatdisplay set in which the surface light source device 0 shown in FIGS. 1and 2 is utilized as back-light. The flat display set is equipped with aframe 21, a display unit 22, a surface light source device (back-lightunit) 0 and a chassis 23. It also has a pair of speakers 24 and 25, ashield cover 26 and a rear cover 27. The frame 21 is located in thefront of the set, and the window portion 28 is provided. The displayunit 22 has a flat shape, and is of a transmission type. It is installedto the frame 21 from behind, and matches to the window portion 28 toconstitute a screen. The chassis 23 is located in the back of the set,and is engaged with the frame 21 with the display unit 22 interposedtherebetween to form a flat containing space 29 on the back side of thedisplay unit 22. The back-light unit is a surface light source device 0previously assembled using a housing 1 having a flat shape, and can bedetachably inserted into the containing space 29 described above toilluminate the transmissive display unit 22 from the back.

As described above, on the upper side portion 7 of the housing 1, anopening 7a is formed. In this respect, on the lower side portion 7 ofthe housing 1, an opening 7b corresponding thereto is formed though notshown. Further, when the housing 1 is mounted to the containing space 29of the chassis 23, an opening 23a is formed on the upper side portion ofthe chassis 23 so as to match the opening 7a. On the lower side portionof the chassis 23, an opening is formed correspondingly to this opening23a. Though not shown, an air-cooling fan is mounted on the upper sideof the flat display set so that cooling air is forcibly fed into theinterior of the surface light source device 0 through the openings 23aand 7a to perform effective air-cooling. In this respect, in the presentembodiment, in order to facilitate the maintenance such as lampreplacement, there is adopted such structure that the surface lightsource device 0 is manufactured into a cassette so as to be detachablyinserted into the chassis 23. However, the present invention is notrestricted to this, but the surface light source device may be installedwith the chassis 23 itself as the housing. In this respect, a circuitsubstrate 30 for driving the display unit 22 is mounted on the back sideof the chassis 23.

FIG. 4 is a sectional view schematically showing an example of atransmissive display panel installed in the display unit 12 of the flatdisplay set shown in FIG. 3. This display panel is of a plasma addresseddisplay type, and has flat panel structure consisting of a liquidcrystal cell 101, a plasma cell 102 and a common intermediate substrate103 interposed between the two. The intermediate substrate 103 consistsof exceedingly thin sheet glass or the like, and is called micro-sheet.The plasma cell 102 is composed of a lower substrate 104 consisting ofglass or the like joined to the intermediate substrate 103, and the airgap between the two is charged with ionizable gas. On the inner surfaceof the lower substrate 104, stripe-pattern discharge electrodes 105 areformed. Since they can be printed and baked on a flat glass substrate104 by the screen printing method or the like, the discharge electrodes105 are excellent in productivity and workability and also can be madefine. On the discharge electrodes 105, partition walls 106 are formed,and divide the air gap which has been charged with ionizable gas toconstitute discharge channels 107. These partition walls 106 can be alsoprinted and baked by the screen printing method, and their apexes are incontact with one surface side of the intermediate substrate 103. Thestripe-pattern discharge electrodes 105 alternately function as eitheranode A or cathode K to cause plasma discharge between the two. In thisrespect, the intermediate substrate 103 and the lower substrate 104 arejoined together through glass frit 108 or the like.

On the other hand, the liquid cell 101 is composed of the uppersubstrate 109 consisting of glass and the like. This upper substrate 109is adhered to the other surface side of the intermediate substrate 103through a predetermined gap by sealant 110 or the like, and the gap ischarged and filled with liquid crystal 111. On the inner surface of theupper substrate 109, a signal electrode 112 consisting of transparentconductive film is formed. This signal electrode 112 is orthogonal tothe stripe-pattern discharge electrode 105. At the intersection portionbetween the signal electrode 112 and the discharge channel 107, amatrix-shaped pixel is prescribed.

In a plasma addressed display panel having such structure, a line-shapeddischarge channel 107, in which plasma discharge is performed, isswitched in line sequence for scanning, and an image signal is appliedto a column-shaped signal electrode 112 on the liquid crystal cell 101side in synchronism with this scanning to thereby perform displaydriving. When plasma discharge occurs within the discharge channel 107,the interior has almost uniformly anode potential to select pixel foreach line. In other words, the discharge channel 107 functions as asampling switch. When an image signal is applied to each pixel while theplasma sampling switch is conducting, the sampling is performed and thetransmission factor of pixels can be controlled. Even after the plasmasampling switch enters a nonconducting state, the image signal is heldas it is within the pixel. If a plasma addressed display panel havingsuch structure is back-lighted by a surface light source deviceaccording to the present invention, a clear image will be projected onthe front.

As described above, according to the present invention, the closed space(lamp house) is formed by the diffuser panel and the reflective platewhich have been installed in the housing, and lamps are housed withinthe closed space. On the other hand, the open space is formed betweenthe reflective plate and the housing, and cooling air is forcibly fedhere by an external air-cooling fan or the like to diffuse the heatgenerated from the lamps outward. Since no cooling air enters the closedspace where the lamps are arranged, dust and dirt can be effectivelyprevented from adhering. Also, since the cooling air flows along theback surface of the reflective plate, it is possible to effectivelyremove the heat from the lamps.

What is claimed is:
 1. A display device, comprising:a frame located at afront of said display device and being formed with a window portion; adisplay unit being a flat transmissive panel; a back-light unit beingdevice having:a housing having a window portion located ahead, a baseportion located behind and side portions forming a flat space byconnecting together the two; a diffuser panel mounted to said windowportion; a reflective plate supported by said side portions, forpartitioning said flat space into a closed space ahead and an open spacebehind to be interposed therebetween; lamps housed in said closed space,and positioned right above said reflective plate and right under saiddiffuser panel to radiate light toward said diffuser panel; an electriccircuit portion housed in said open space, for being electricallyconnected to said lamps to light them up; and heat-radiating portionsformed in said side portions of said housing, including a number ofopenings for conductively connecting to said open space, for introducingcooling air supplied from outside into said open space to diffuse heataccumulated within said housing; and a chassis located behind the setfor matching the frame to interpose the display unit therebetween.
 2. Adisplay device as defined in claim 1, wherein said transmissive panelused for said display unit is a plasma addressed display.